Method of coating metal and article produced thereby



June 14, 1950 s. GUSMAN EI'AL 2,940,872

METHOD OF COATING METAL AND ARTICLE PRODUCED THEREBY Filed Aug. 28, 1957 Copolymer of Methyl or Ethyl Me'rhucrylafe and I96 to IO% of a -(Q-C Alkylaminoelhyl Acrylote or Mefhucrylafe.

Thermosei Prime r I United States ?atent Ofiice Patented June 14, 1960 METHOD OF COATING METAL AND ARTICLE PRODUCED THEREBY Samuel Gusman, Wyncote, and Sidney Melamed, Philadelphia, Pa., assignors to Rohm & Haas Company, Philadelphia, Pa., a corporation of Delaware Filed Aug. 28, 1957, Ser. No. 680,672 19 Claims. Cl. 117-75 This invention relates to lacquers and lacquer finishing. It is particularly concerned with new lacquer compositions based on certain methacrylate copolymers and adapted to be applied by commercial spraying techniques. It is also concerned with the finishing of surfaces, especially of metals, with the lacquers of the present invention.

Poly(rnethyl methacrylate) is highly regarded as a coating material because of its durability, particularly its high retention of gloss and color, when pigmented, during prolonged outdoor exposure. Because of this quality, it has long been desired to use poly(methyl methacrylate) lacquers for the finishing of automobile bodies as well as other metallic articles subject to outdoor exposure. However, such lacquers have poor adhesion to metals directly and also poor adhesion to coatings obtained from primers of the baking type. While their adhesion to such primers can be somewhat improved by roughening of the exposed surface of such primer coatings, as by a sanding operation, and such toughening is frequently resorted to in any event to improve adhesion, the improvement thereby obtained is not as pronounced as would be desirable nor is it practical to roughen the primer in all of the indentations that are present in such structures as automobile bodies. It is characteristic of this system that the adhesion of the poly(methyl methacrylate) to the primer improves with age. Very shortly after application, however, there is insuflicient adhesion between the primer coating and the poly(methyl methacrylate) coating to allow the application of masking tape when a multi-color pattern of decoration is desired. In such an event, the masking tape, when removed, removes the poly(methyl methacrylate) top coat. For this reason, the application of poly(methyl methacrylate) is restricted.

Consequently, when poly(methyl methacrylate) lacquers are applied, a non-baking type of lacquer is generally applied as a primer or as an intermediate coat between the primer of baking type and the poly(methyl methacrylate) lacquer. Common non-baking lacquers that may be so used contain nitrocellulose, such as a solution of nitrocellulose and a plasticizer therefor with or without additional film-forming materials, such as polyvinyl butyral.

In accordance with the present invention, it has been found that the incorporation of 0.5% to by weight, based on the total weight of the copolymer, of dimethylaminoethyl methacrylate into lower alkyl methacrylate polymers markedly enhances the adhesive properties of the polymers toward baking primers in general so that lacquers made therefrom can be applied directly over a baking primer without the necessity to employ an intermediate or sealer coat of a non-baking type. Preferably, to obtain the optimum adhesion in conjunction with outdoor durability, the lacquers of the present invention are based on the use of copolymers of lower alkyl methacrylate with 2% to 4% in the polymer molecule ofdimethylaminoethyl methacrylate. The lacquer may contain an external plasticizer for the polymer or the polymer may be itself modified by the incorporation of flexibilizing comonomers so that the copolymer in the lacquer contains three or more different comonomer units and is internally plasticized by virtue of certain of those units. This is particularly true when the copolymer is derived from methyl methacrylate. If desired, an internally plasticized copolymer of methyl methacrylate and dimethylaminoethyl methacrylate may be used in conjunction with an external plasticizer as well.

The single figure of the drawing is a perspective view of one embodiment of the invention partially in crosssection and with parts cut away.

The lower alkyl methacrylates with which the invention is particularly concerned are methyl methacrylate, and ethyl methacrylate.

The invention, therefore, contemplates the incorporation in a finishing lacquer within suitable solvents with or without external plasticizers of either binary copolymers containing to 99.5% by weight of the lower alkyl methacrylate (or a mixture of them) with 10% to respectively, of dimethylaminoethyl methacrylate or of copolymers of ternary, quaternary, etc., character contaiuing at least 50% by weight of methyl methacrylate, or ethyl methacrylate or a mixture of these two esters, /z% to 10% by weight of dimethylaminoethyl methacrylate and the balance of one or more other copolymerizable materials. These copolymerizable materials may be any monoethylenically unsaturated comonomers including acrylonitrile, methacrylonitrile, styrene, vinyl acetate, or, in small amounts up to 2%, an acid, such as acrylic acid, methacrylic acid, or itaconic acid. When the comonomers just mentioned form the balance of the copolymer of the lower alkyl methacrylate and dimethylaminoethyl methacrylate, it is generally necessary to employ an external plasticizer to obtain proper flexibility. However, the copolymer may be internally plasticized to any desired extent by incorporating with the lower alkyl methacrylate and dimethylaminoethyl methacrylate one or more of the following comonomers: ethylene, isobutylene, esters of acrylic acid with alcohols having from 1 to 18 or more carbon atoms, such as methyl alcohol, ethyl alcohol, butyl alcohol, n-octyl alcohol, t-octyl alcohol, dodecyl alcohol, hexadecyl alcohol, octadecyl alcohol, and so on or esters of methacrylic acid with alcohols having 3 to 18 carbon atoms. If desired, the copolymer of methyl or ethyl methacrylate and dimethylaminoethyl methacrylate may contain units from both an internally plasticizing comonomer of the list just mentioned and one of the comonomers mentioned in the first list above. As stated previously, when a plasticizing comonomer is included, it may be unnecessary to include an external type of plasticizer in the lacquer.

The viscosity average molecular weight of the lower alkyl methacrylate copolymers may be in the range of 40,000 to 150,000 and is preferably between 90,000 and 130,000. By using copolymers in these ranges and especially in the latter of them, itis possible to produce sprayable lacquers of high solids, such as from about 12 to 20% by weight of non-volatile solids concentration. The copolymers may be prepared by granular, emulsion, or solution polymerization of the several comonomers and, if desired, a portion having a preferred narrowrange of molecular weight may be extracted from the products of such polymerization procedures by preferential solvent techniques in accordance with well-known practice. A preferred method of preparing the copolymers involves introducing suitable proportions of the comonomers with a solvent which may be a solvent for both the monomers and the copolymer and with a catalyst, .such asoneof 3 r the well-known organic peroxide catalysts, such as benzoyl peroxide, as u,a'-azodiisobutyronitrile, into a reaction vessel in which the mixture is heated withcontinuous agitation for 'a'period' of 2 to 9 hours -f ollowedby cooling. i The lacquer may contain one or more external plasticizers in an amount 'up" to 50% by weight of the weight of the copolymer. "Examples of plasticizers that'lare suita ble include beniyl biityl phthalate, dibutylfphthalate, 'trijphenyl phosphate, 2 ethyl hexyl benzyl phthalate and dicyclohexyl phthalate.

employed include diallyl phthalate, dibenzyl phthalate, butyl cyclohexyl 'p'hthalate, mixed ben'zoic acid and fatty oil acid esters of pentaery thritol poly (propylene adipatej dibenzoate, diethylene glycol dibenzoate, tetrabutylthiodisuc'ciiiate, butyl phthalyl butylglycolate, acetyl tributyl citrate, dibenzyl sebacate, 'tricresyl phosphate, toluene ethyl sulfonam'ide, the di 2 -ethylhexyl ester of hexarh eth ylene diphthalate,and di(methylcyclohexyl) phthalate. The particular plasticizer and the amount thereof used are chosen in accordancewith thedemand for com-. patibility. f

' Various solvents may be employed, such as toluene, xylenes, acetone, methyl ethyhketone, methyl isobutyl ketone, methyl isopropyl ketone, amyl alcohol, 2-ethoxyethyl acetate, ethyl acetate, butyl lactate, amyl acetate, methyl acetate, denaturedthyl alcohol, isopropanol, diacetone alcohol, cyclohexanol, ethylene dichloride, diisobutyl' ketone,-'cyclohexanone, Z-butoxyethanol, f urfuryl, petroleum naphtha, boiling in the range of about 87 to about 145 C.,"cyclohexane,- hexane, aromatic hydrocarbon mixtures, such as "Solvesso 150, and also various aliphati naphthenic and aromatic naphthas. While certain of these' 'solvents cannot be used alone because of lack of solvent' power for the copolymers but they can in amixture with others. Obviously, mixtures of such solvents "are generafly quite useful.

The baking primer coats over which the copolymers of the'pres'ent inventionmay be applied include the drying oil-modified alkyds, rosin-modified alkyds, mixed or coreacted' allcyds and aminoplast's, mixed orco-reacted alkyds 'and epoxy'fresins, mixed or 'co-reacted alkyd/ aminopla st/ep oxy resins, mixed or co-reacted epoxidized esters of higher fatty acids with'aminoplast resins and so on. The incorporation of the dimethylaminoethyl metha cr-ylate has been found to improve the adhesion of j the lower alkylmethacrylate'copolymers obtained without appfeciably'modifyingthe good qualities of the lower alkyl methaerylate polymer coating, especially 'in respect to hardness, flexibility, and durability 'of gloss and color on outdoor exposure. The adhesion has been found to be enhanced with respect to baked primers so that the use of masking tape in the application of multi-color designs has been found permissible. The use of a greater proportion of dimethylaminoethyl methacrylate than l% by weight has been found to be undesirable because of noticeable loss in the desirable qualities obtained from the lower alkyl metha'crylate component in the coatings. Generally, the optimum qualities of adhesion anddurability of gloss andcolor are obtained when the dimethylaminoethyl 'methacrylate isused in the range of about 2% to 4% by weight of the copolymer and, accordingly, this range is preferred." v It has been found. that the copolymer with dimethylaminoethyl methacrylate is quite distinctive in its quality of adhesion to. the baking type of primers generally. With copolymers of the present invention, the adhesion to such primers is of such strong quality that it is frequentlynot even necessary to roughen the primer before. applicavtion ofltheila'cquers of'the present invention in-order to get' adequate adhesion even. sufficient to allow the appli:

Other well-known plasticizers for polymers of methyl-and ethyl methacrylates which may be or one of the well-known azo catalysts, su'chproduced which are of the same constitution except that the dimethylaminoethyl methacrylate is replaced with diethylaminoethyl methacrylate, the adhesion obtained on the baking type primer in most'instances is reduced to such an extent that it is essential to roughen the surface of such primers to obtain adequate adhesion between the top coat and the primer and even with the toughening, e adhe n is s e mes' n fl nt o p rm t h use of masking tape shortly after the drying of the coating.

While, for certain purposes, a clear lacquer may be employed, it is quite general to include pigments in an amount up to 100% by Weight of the polymer in the lacquer finishing compositions. Examples of suitable pigments include titanium dioxide, carbon black, iron blues, phthalocyanine blues and greens; metal oxides, hydroxides, sulfides, sulfates, silicates and chromates; organic maroons, aluminum flake, bronze powders, pearl essence, and various fillers or extenders such as talc, barytes, china clay and diatomaceousearth. V I

It will be obvious to those skilled in the organic coating art that the amount of pigment may be varied widely, depending on the effect desired. The amount of pigment, by weight based on the weight of the organic film-forming material, may vary between about 2% for light, highhiding pigments, such as carbon black, and about 100% for heavy, low-hiding pigments such as lead chromate.

It is common practice in thecoating art to prepare liquid coating compositions on a commercial basis in a highly concentrated form. In comparison with the same composition in a thinned or diluted form ready for application, the concentrated form is more resistant to pig rnentsettling during storage, is cheaper to storeand ship because less weight and space are involved, and is in admixing appropriate organic liquids form a part of this 7 invention. The maximum degree of concentration, i.e.

the non-volatile solids content, is limited only by the maximum consistency which can be conveniently handled by the manufacturer and the ultimate user.

v While concentrated lacquers having a nOn-volatile'solids cation of masking tape shortlyafter the drying of the topcoat to permit the application of a multi-coloridesigu. When. copolymers o'f methyl or etbyl 'methacrylate. are

content'of 75% by weight, or even higher, may be prepared; the normal concentration is usually between 30 and "60%, The minimum concentration isobviously the solids'content; of the re'ady-to-apply lacquers; but, as pre /i ously-mentioned, such compositions are'not usually pre: pared by the manufacturer because they are not adaptable to adjustment'by the user The method of dispersing or grinding pigment in the film-forming materials is not critical provided a smooth, uniform dispersion of finely divided pigment is produced. Examples of suitable equipment well known in the art areball, pebble, 'buhrstone,roller, EDd'CQllOldfHllllS and kneader mixers, such as Banbury or WaIner-Pfleiderer.

The concentrated lacquers may be redhced to whatever concentration is suitable for the particular manner of ap* plication; The application concentration may vary from about 5 to 30% non-volatile solids (that is, including plasticizer), depending upon the manner ofapplication and-"the thickness Qfcoating desired. For spraying, the concentration may be between 10 "and 20% solids.

While the preferred lacquers ofi'tbis invention contain, as film-forming materials, only copolymers ofmethyl or ethyl 'methacrylate of the present invention andplasth cizers therefor; suitable lacquers may be prepared by incorporating other compatible film-forming materials With'theaforementioned ingredients; Examples'oi such additionalifilm forrning materials are cellulose nitrate, othercellulo'se ester's, alkyd resins, and polymers of-the short chain alkyl' esters of acrylic and methacr-ylicacids other than polym'eth'yl methac rylate, the choice being dictated:bytherequirement for-compatabiliw. Obviouslyv it is most convenient to incorporate the additional fi1m forming materials in the form of solutions.

The coatings may be air-dried under normal conditions of atmospheric temperature and humidity with good ventilation. Air-drying to a stage which permits handling may require 4 to 24 hours. Higher temperatures of drying may be employed, such as from about 140 to about 300 or more. The use of such elevated temperatures reduces the drying time so that drying at 150 to 200' F. may be fully accomplished in 30 to 60 minutes whereas the use of 250 to 300 F. generally shortens the time considerably.

Although the coating compositions of the present invention have been found to have advantageously improved adhesion to primed metals, nevertheless, they are also useful for applying decorative and protective coatings to anticles manufactured from a variety of materials, such as wood, metal, ceramics and other organic and inorganic substances. While conventional air spraying is the preferred method of applying the products of this invention, obviously other methods may be used, such as hot air spraying, steam spraying, electrostatic spraying, spraying a preheated coating composition, dipping, brushing, and roller-coating.

The copolymers of the present invention containing /2.% to 10% by weight of the amine groups mentioned may be mixed, to the extent they are compatible, with similar polymers which contain no amine groups the amounts of the polymers being such as to provide from A: to 5% (by weight) of amine-containing units in the overall composition of the polymer blend. The preferred proportion of such amine-containing units is from about /2 to 2% of the overall weight of the polymer blend.

In the drawing reference numeral 2 indicates the metal base upon which there is imposed in adherent contact therewith a thermoset primer coating 3. On the primer coating 3 there is shown the topcoating of the copolymer of the alkylamino-ethyl acrylate or methacrylate which is adherent to the primar layer.

In the following examples which are illustrative of the present invention, the pants, percentages, and ratios are by weight unless otherwise indicated. In the examples following, the adhesiveness was tested by scribing X-shaped markes in the coating, applying Scotch tape to the marks, pressing the tape firmly against the coated surface by rubbing with a rubber, pencil eraser. The tape is then removed by lifting while pulling in a direction parallel to the plane of the surface so that the angle the tape makes as it leaves the surface is a small acute angle on the order of 15. The test is done at two periods, the first about to 30 minutes after the completion of the baking of the topcoat, the coating being cooled before application of the tape, and the second a day later.

Example A A solution comprising 949 parts of methyl methacrylate, 51 parts of dimethylaminoethyl methacrylate, 2.5 parts of azobisisobutyronitrile and 670 parts of toluene is added in the course of two hours to a five liter flask maintained at 80 C. by means of external heating. The mixture in the flask is stirred during the addition and subsequent reaction and maintained at 8085 C. The mixture is then diluted with 830 parts of toluene over a two-hour period, while stirring is continued at a temperature of 8082 C. Heating and stirring are continued for a total of 12 hours and the mixture diluted with toluene to 30% resin solids (approximately 830 parts of toluene). The Gardner-Holdt viscosity is 0 (3.7 poises). The copolymer contains approximately 5.1% of dimethylaminoethyl methacrylate.

Example B The procedure of Example A is repeated substituting for the comonomers, 954 parts of methyl methacrylate and 46 parts of diethylaminoethyl methacrylate. The ee- .polymer contains approximately 4.6% of diethylamino ethyl methacrylate and is dissolved at 30% solids in toluene.

Example C The procedure of Example A is repeated substituting for the comonomers 725 parts of methyl methacrylate, 210 parts of ethyl acrylate, and 65 parts of dimethylaminoethyl acrylate yielding a copolymer containing 6.5% of the last-named comonomer.

Example D The procedure of Example A is repeated substituting for the comonomers 800 parts of ethyl methacrylate, parts of butyl acrylate and 100 parts of dimethylaminoethyl methacrylate yielding a copolymer containing about 10% of the last-named comonomer.

Example E A blend is made by mixing 500 parts of a homopolymer of methyl methacrylate with 500 parts of copolymer (solids) obtained in Example A. Each is dissolved in toluene so that the mixture is a 30% solution of polymer solids in toluene.

Example F Example 1 A primer is prepared by ball-milling a mixture of 156 parts of iron oxide, 78 parts of zinc chromate, 26 parts of micronized talc, 210 parts of a 60% solids solution in mineral thinner of a drying alkyd of medium oil length based on linseed oil, phthalic anhydride, and glycerol, 28 parts of a 50% solids solution in a 1:4 mixture of xylol and n-butanol of a butylated polymethylol melamine, and 100 parts of a 2:1 mixture of xylol and mineral thinner, and subsequently reducing the ball-milled mixture to a viscosity of 18 seconds in a No. 4 Ford cup with a 2:1 mixture of xylol and mineral thinner. The resulting primer having a 65 to 35 Weight ratio of pigment to binder is coated by spraying on phosphatized (Bonderized) steel panels, air-dried 15 to 30 minutes, baked 45 minutes at 275 'F., and cooled. Then the panels are sanded while wet with water, rinsed with water, and dried in an oven at 200 F. .for 10 minutes. After sanding, the coating is approximately 1 mil in thickness.

A pigment paste is prepared from a mixture of 44.55 parts of rutile titanium dioxide, 0.45 part of lampblack, 45 parts of the 30% solution in toluene of the copolymer of methyl methacrylate and dimethylaminoethyl methacrylate of Example'A, and 10 parts of Z-ethoxyethyl acetate by making four passes of such mixture through a roller mill. Then 40 parts of the resulting paste is mixed with 80 parts of the 30% copolymer solution obtained in Example A, 12.6 parts of butyl benzyl phthalate and 169 parts of a solvent composed of a 30/35/35 blend of Z-ethoxyethyl acetate, toluene, and methyl ethyl ketone to produce a lacquer having a 12-second No. 4 Ford cup viscosity.

The lacquer is sprayed over the primed steel panels, air-dried 3 to 5 minutes, and a second spraying of the lacquer is then made. This is then air-dried 15 to 30 minutes and then baked 30 minutes at 180 F.

On testing for adhesion as described above, substantially no removal of the coating occurred. However, similar coated panels (control) in which the to -coating was formed in the same way using instead of the copolymer.

solution of Example A, a 30% solution in toluene of a polymer of methyl methacrylate containing no aminecontaining units showed substantially complete removal of the coating. 7 I r and'thesolution of melamine condensatefisomitted.

Example 2 f rnapmc a m oiExaLmple 1 is repeated, st bsamasgi for the two doses-'"of the copolymersolution of Example A the same amounts of the copolymer solution obtained in Example B containing" about 4.6% of diethylaminoethyl me a yl ei il r s l s. re b ine h P edure- 9 E mpl peated, om n t sanding of the primer, and substitutihg for thellq parts of alkyd resin solution and the28 parts of butylated polymethylol melamine the following? 2110'- parts of, asolutioh (60%, solids) inzxylol oftihe an ciliaity, acid modified epoxy-alkyd obtained by: the. condensation of an isopropylidene-bis 'plrenollepichlorohydrin pondensate.WithJglycemhand phthalic .acid anhydride and 28 parts ofia'solution. (at.'5i0% solids) in a 1:1 mixture of xylol andnrbuta-nol'of a butylated polymethylol urea.

Substantially no removal occurred on adhesion test. Whereas coated panels made 'in the same way using in place of the copolymersolution of Example A, a- 30% solutionj in toluene of a homopolymerof methyl; methacrylate show substantially complete removal of the coatmg.

Example 4 The procedure of Example 1 is repeated except that the sanding operation is omitted andthe primer is made from 126 parts iron oxide I 154 parts barytes 180 parts of the alkyl solution of Example 1 2 4 parts of the melamine condensate; solution of Ex ample l a "-On testing, substantially no removal of coating is pro:

.duced. Whereas the control panel shows substantially.

complete removal, such control panels being obtained the sameway but substituting for the copolymer solutiodoflixarnple A, a 30% solution in toluene of. poly (methyl methacrylate). V p I a V Example 5 The procedure of Example 1 is repeated except that the alkyd'solution of the primer is increased'to 233 parts Onrtesting for" adhesion, substantially no removal ofthe coating occurred, whereas control anels'made in thej same way substituting poly(me thyl vr'nethacrylate'),forthe copolymer 'of Exmplei show extensive removal of; coating.

li xan zp le 6 7 Q A (I The procedure of Example '3 is repeatedexcept that V thei'ureagcondens'ate-is omitted from the primer and the amount of the epoxy-alkyd is increased from 210 parts tol225'partsg Good adhesion is obtained comparable to the improvement obtained'by Example 3.

i Example 7 The procedure ot' Example 1 is repeated-substituting correspondingamounts of the copolymer' solution of Example are: that of Example A wherever used. Excellent adhesion is obtained.

. Example 8 corresponding amounts of the copolymer. solution of. Ex-.

fun

Good adhesion results, the improvement being compara= ble to that obta' don steel panels-by, Example 1.

r 'l he procedure oip lixample is repeated, I except that thesteel panelsiwer'e replaced by burnished copper, brass, andMonel metalpanels with excellent results.

n. 1 ExamplelO' Theprocedure. ofExample 1' is repeated except that the; copolymer solution of Example E is used in place of-th ecopolymersplution. of Example A. The improvementzin adhesion: is comparable to that obtained in Exampletl. a

Insteadof'th'e methacrylates of dimethylaminoethanol anddiethylaininoethanol, the acrylates may be used.

Weclaim:

1. As an article of manufacture, a metal base, a baked primer coating on the surface of the rnetal the binder of'said coating being formed from a thermosettin'g resin, and, superimposed on the primer coating, a coating of a copolymer ofgan ester selected from the group consisting of methyl methacrylate and ethyl methacryIate and' 1% to 10% by Weight of copolymerized units selected from thegroup consisting of dimethylaminoethyl acrylate and methacrylate and diethylaminoethyl acrylate and methacrylate.

2. As an article of manufacture, a metal base, a baked primer coating on the surface of the metal, the binder of said'coating being formed from a thermosetting resin, and, superimposed on the primer coating,1a coating of a copolymerQhaving a viscosity average. molecular'weight of 40,000 to 150,000, of an ester selectedfrom the group 7 consisting of methyl methacrylate and ethyl methacrylate and 1% to 10%-byweight of copolymerized units selected from the group consisting of dimethylamincethyl acrylate and methacrylate andcliethylaminoethyl aciylate and methacrylate. I

3 As an article of manufacture, a metal base, a baked primer coating comprising an alkyd resinonthe surfacefl of themetal, and, superimposed onthe primer coat ing,' a coating of a copolymer of an ester selectedfrom the grou'pconsisting" of methyl methacrylate and ethyl methacrylate and 1%" to 10% by weight 'of copoly'merized units, selected from the group consisting of dimethylaminoethyl acrylate' and methac'rylate and diethylaminoethyl acrylate-an'tl mthacrylate. Y

4, As an article of mauufacture a metal base, a baked primer coating comprising an aminoplast resin on-the surface of the, metal, and, superlmposecl' on the primer cpating,-ia coating of .a copolymer of an ester selectedample C5for that of Example A wherever used and anodii ed aluminum is used instead of phosphatized'steel from the group consisting'of methyl me tha'crylate and ethyl methacrylate and 1% to 10% by'weight of copolymerized units selected from the'group consisting of dirnethylaminoethyl acrylate and methacrylate and diethylaminoethyl'acrylate and methacrylate. 1 p 1 5 a As an-article ofmanufacture, a metal base, a baked primer-coating; comprising a drying-oil modified alkyd onthe suriaeeof the metal, and, superimposed on the primer. coating, a coating ofa copolymer of an ester selected. from thegroup consisting of methyl methacrylate and et hyl methacrylate and 1% to 10% by weighttof copolymerlzed units selected fromthe group consisting ofdimethylaminoethyl acrylate and methacrylate, and. diethylaminoethyl acrylate and methacrylate.

' 6. As an article of manufacture, a metal base, a baked primer coating comprising an epoxy-modified alkyd on the-surface'of themetal, and, superimppsedlon the primer -coating;-a"coating'of a copoly'me'rfof ester'selected from the group consisting of methyl methacrylate and ethyl methacrylate and 1% to 10% by weight of copolymerized units selected from the group consisting of dimethylaminoethyl acrylate and methacrylate and diethylaminoethylacrylate and methacrylate.

7. As an article of manufacture, a metal base, a baked primer coating comprising a mixture of an alkyd and an aminoplast resin on the surface of the metal, and, superimposed on the primer coating, a coating of a copolymer of an ester selected from the group consisting of methyl methacrylate and ethyl methacrylate and 1% to 10% by weight of copolymerized units selected from the group consisting of dimethylaminoethyl acrylate and methacrylate and diethylaminoethyl acrylate and methacrylate.

8. As an article of manufacture, a metal base, a baked primer coating comprising a mixture of an alkyd and an alkylated polymethylol melamine on the surface of the metal, and, superimposed on the primer coating, a coating of a copolymer of an ester selected from the group consisting of methyl methacrylate and ethyl methacrylate and 1% to 10% by weight of copolymerized units selected from the group consisting of dimethylaminoethyl acrylate and methacrylate and diethylaminoethyl acrylate and methacrylate.

9. As an article of manufacture, a metal base, a baked primer coating comprising a mixture of an alkyd and an alkylated polymethylol urea on the surface of the metal, and, superimposed on the primer coating, a coating of a copolymer of an ester selected from the group consisting of methyl methacrylate and ethyl methacrylate and 1% to 10% by weight of copolymerized units selected from the group consisting of dimethylaminoethyl acrylate and methacrylate and diethylaminoethyl acrylate and methacrylate.

10. As an article of manufacture, a metal base of steel, a baked primer coating on the surface of the metal, the binder of said coating being formed from a thermosetting resin, and, superimposed on the primer coating, a coating of a copolymer of an ester selected from the group consisting of methyl methacrylate and ethyl methacrylate and 1% to 10% by weight of copolymerized units selected from the group consisting of dimethylaminoethyl acrylate and methacrylate and diethylaminoethyl acrylate and methacrylate.

11. An article as defined in claim 10 in which the binder of the top-coating comprises a copolymer of methyl methacrylate with dimethylaminoethyl methacrylate.

12. An article as defined in claim 10 in which the binder of the top-coating comprises a copolymer of methyl methacrylate with diethylaminoethyl methacrylate.

13. An article as defined in claim 10 in which the binder of the top-coating comprises a copolymer of ethyl methacrylate with dimethylarninoethyl methacrylate.

14. An article as defined in claim 10 in which the binder of the top-coating comprises a copolymer of ethyl methacrylate with diethylaminoethyl methacrylate.

15. An article as defined in claim 10in which the binder of the top-coating comprises a copolymer of methyl acrylate, ethyl acrylate and dimethylaminoethyl methacrylate.

16. A method which comprises the steps of applying a coating of a baking type primer to a metal substrate, the binder of said coating being formed from a thermosetting resin, drying and baking the primer, and subsequently applying to the coating obtained from the primer a solution in an organic solvent of a copolymer of an ester selected from the group consisting of methyl methacrylate and ethyl methacrylate and 1% to 10% by weight of copolymerized units selected from the group consisting of dimethylaminoethyl acrylate and methacrylate and diethylaminoethyl acrylate and methacrylate and then drying the coated metal.

17.v A method which comprises the steps of applying a solution of a thermosetting resin to the surface of a metal, drying the solution to form a coating on the metal, baking the coated metal to convert the coating to an infusible and insoluble condition, applying to the infusible coating a solution in an organic solvent of a copolymer of an ester selected from the group consisting of methyl methacrylate and ethyl methacrylate and 1% to 10% by weight of copolymerized units selected from the group consisting of dimethylaminoethyl acrylate and methacrylate and diethylaminoethyl 'acrylate and methacrylate and then drying the coated metal.

18. A method as defined in claim 17 in which the copolymer is a copolymer of methyl methacrylate with 0.5% to 10% of dimethylaminoethyl methacrylate.

19. A method as defined in claim 17 in which the copolymer is a copolymer of methyl methacrylate with 0.5% to 10% of dimethylaminoethyl methacrylate and the thermosetting resin is an alkyd.

References Cited in the file of this patent UNITED STATES PATENTS 

1. AS AN ARTICLE OF MANUFACTURE, A METAL BASE, A BAKED PRIMER COATING ON THE SURFACE OF THE METAL, THE BINDER OF SAID COATING BEING FORMED FROM A THERMOSETTING RESIN, AND, SUPERIMPOSED ON THE PRIMER COATING, A COATING OF A COPOLYMER OF AN ESTER SELECTED FROM THE GROUP CONSISTING OF METHYL METHACRYLATE AND ETHYL METH- 